Radio communication system



July 31, 1934. E. L. KOCH RADIO COMMUNICATION SYSTEM Original Filed Dec. 51. 1929 2 sh t -sheet Max 7| llll II Wbk Enventon EARL L. KOCH.

E. L. KOCH July 31, 1934.

RADIO COMMUNICATION SYSTEM Original Filed Dec. 2 Sheets-Sheet 2 Zhwentor EARL L.KOCH.-

BB 5 I a W Cittorneg Patented July 31, 1934 1,968,458 RAEHQ CQIt EMUNIICATION SYSTEM Earl L. Koch, Chicago, Ell, assignor, by mcsne as- I sacraments, to Earl L. Koch Holding-Corpora-. tion, New york, N. Y... a corporation of New York Original application December 31, 1929, Serial No.

Divided and this application March 31, 1931, Serial No. 526,653

l Claims.

This invention relates to high frequency radio communication systems, and it has among its objects the provision of improved radio transmitting and radio receiving systems capable of operating on much narrower frequency bands than those used heretofore, and thereby enabling the establishment of a much larger number of practically useful communication channels within the available radio spectrum. This application is a division of application Serial N umber 417 ,684, filed December 31, 1929.

The novel features and principles of the invention will best be understood from the following description of a radio communication system exemplifying the invention, reference being had to the accompanying drawings wherein Figs. 1 and 2, when placed end to end, with Figure 1 to the left, illustrate a five channel radio receiving system embodying the invention.

In point to point radio telegraph communication systems, messages are transmitted over definitely assigned frequency channels which are allocated to the stations of the systems. Each channel is of a definite mean frequency and the stations operating within the channel are not permitted to deviate from this mean frequency beyond a predetermined degree.

At the present time. there is available for point to point communication systems in the high frequency range the frequency band extending from 1500 kilocycles to 23,000 kilocycles. Of this frequency range, the band extending from 1500 kilocycles to 6000 kilccycles is known as the continental high frequency band and has been assigned for use in point to point communication over the continent.

In the present state of the art, it is generally considered that the separation between the mean frequencies of the individual communication channels in these bands must be 0.2% of the frequency assigned to a particular channel. Thus, a channel having an assigned frequency of 6,000 kilocycles must include a frequency band of 12 kilocycles; ihe communication system of the present invention has been developed for use in communication over channels in the continental high frequency band and has proven to be capable .of practically operating with a channel separation which is only one-fifth of the channel separations heretofore deemed practicable. However,

the invention is not limited to this specific increase of the channel number practicable Within the range of frequencies available for commercial use, nor to the particular frequency band, but its features are applicable and useful to improve radio communication systems,to decrease the channel separation necessary for efiicient operation of such systems, and. to generally provide more efficient, simple and reliable radio communication between widely spaced points. Through the use of the invention, it is possible to provide many more communication channels within the available radio spectrum than with the systems known heretofore, each channel being capable of operating without interfering with the adjacent channels and without being disturbed by signals transmitted in these channels.

For purposes of illustration, it is assumed that there was made available for communication purposes one of the official short wave channels, say

a channel having a frequency of 5,875 kilocycles. On the basis of the permissible deviation of 0.2%

of the assigned frequency, this channel will have assigned for its use a frequency band extending from 5869.125 kilocycles to 5880.875 kilocycles. By utilizing the apparatus and arrangements of the invention, I have obtained practical point to point commercial telegraphic communication within the band of frequencies assigned to such channel through five distinct communication subchanneis, each subchannel operating in the same way as a normally assigned channel is intended to operate. In practice, it has been found convenient to have these subchannels separated by a frequency band of 750 cycles, although a larger number of subchannels may be provided within the assigned frequency band by following the principles of the invention.

In the drawings, there is illustrated a five subchannel communication system intended to operate with a frequency separationof 750 cycle'sbetween the individual subchannels. Assuming, for the purpose of illustration, an assigned frequency of 5,875 kilocycles, the individual subchannels are arranged to operate so that the first subchannel operates with a frequency of 5,873.50 kilocycles, the second subchannel with a frequency of 5,874.25 kilocycles, the third subchannel with a frequency of 5,875.00 kilocycles (this being the assigned channel frequency), the fourth subchannel with a frequency of 5,875.75 kilocycles, and the fifth subchannel with a frequency of 5,876.50

:ilocycles.

In the drawings, the five subchannels of the receiving system shown in Figures 1 and 2 are identified by numerals C1 to C5.

The individual subchannels are, in general, provided with the same kind of apparatus, and they are arranged in the same way, so that it will only be necessary to describe in detail the apparatus and arrangement of a single subchannel and point out only its relationship to the apparatus and the arrangements of the other subchannels in order to fully understand the invention.

The receiving apparatus shown in Figures 1 and 2 of the drawings comprises a'reception input amplifier BIA, a reception beat detector RBD, a reception beat amplifier RBA, a reception channel selector RGS, a reception channel amplifier RCA, a reception channel rectifier RGR and a reception relay RE.

The reception input amplifier comprises a screen grid audion tube W1 having a cathode 201, an anode 202, a control grid 203, and a screen grid 204. The input from an aerial AR is impressed upon the input electrodes of tube W1 across an input impedance 205, and an output impedance 206 is connected to the output electrodes of the tube W1, blocking condensers 207 and 208 completing the circuits.

The radio beat detector RBD comprises audion tubes W2, W3, having cathodes 210, anodes 211 and control grids 212, the tube W having also a screen grid 213. A tank circuit GL1 comprising an inductance 215 and a condenser 216 is connected across the input terminals of the tube W2. A tank circuit GL2 comprising an inductance 217, and a condenser 218 is connected in the output circuit of tube W2, by-pass condensers 219 and 220 completing the circuit conections. A nonselective impedance 221 is connected across the input electrodes of audion tube W3, and a primary Winding of an audio frequency coupling transformer 222 is connected to the output electrodes of audion tube W3, by-pass condensers 224 and 225 and high frequency choke coils 226 completing the circuit connections. The two audion tubes W2 and W3 are connected in a reentrant ring circuit similar to the reentrant ring circuit of the transmitter oscillator TO by means of coupling connections 227, 228, including blocking condensers 229, 230. A cathode-heating source 231 and a plate and screen grid bias source 232 completes the circuit connections of the three tubes W1, W2 and W3.

The tank circuits GL1 and GL2 are so adjusted that their frequency differs from the frequency of the received oscillations so that on combination therewith, a beat note of audio frequency will be produced. For instance, assuming that the received frequency is 5,875.00 kilocycles, the tank circuits GL1 and GL2 are tuned for a. frequency of 5872.375 kilocycles so that when the two frequencies are combined a beat frequency of 2625 cycles will result.

I have found that a ring arrangement of tubes such as that described in connection with tubes -W2 and W3, in which the externally received oscillatory input is continuously recirculated together with the local oscillations produced in these circuits, operates as an extremely sensitive beat detector, and that due to the combination of the stable local oscillatory circuit for producing the beats, with effective amplification of the signals differing from the local oscillations, a strong and clear beat oscillation is produced in the output circuit of the tube W3 which, as shown in the drawings, has its input and output circuits untuned, and therefore not discriminating against the individual frequencies. In other Words, by using reentrant ring filter circuit amplification, there is obtained a stable beat oscillation; and the aperiodic character of the input and output circuit of the second audion tube W3 of the ring circuit permits effective amplification of the audio beat frequency so that even very weak incoming signals will give a clear and ample beat note that is suitable for further amplification and reproduction of the signal.

The reception beat amplifier RBA comprises audion tubes W4, W5 having cathodes 235, anodes 236, and grids 237, with associated grid-biasing source 238 and plate source 239, the cathodes being supplied from the cathode supply source 231 referred to before. The output of the audio frequency coupling transformer 222 of the radio beat detector RBD is impressed upon the input electrodes of amplifier tube W4, and the output of this tube is impressed through the audio frequency coupling transformer 240 upon the input electrodes of the second amplifier tube W5. The output of the latter tube is impressed upon a coupling transformer 241 which delivers through conductor 242, amplified beat frequency currents to the radio reception channel selector RCS.

The reception channel selector RCS comprises screen grid tubes W6 and W7 having cathodes 251, anodes 252, control grids 253, and screen grids 254, with associated cathode heating source 255, plate current source 256, audiofrequency choke coils 257 and by-pass condensers 258, 259. Tank circuits GL6, GL7 composed of inductances and condensers are connected to the output elec trodes by the audion tubes W6 and W7, and adjustable-tap input impedances 261, 262 are connected in the input circuits of the two tubes respectively. The amplified audio beat frequency currents derived from the output transformer 241 are impressed through conductor 242 upon the input impedance 261 of audion tube W6 which serves to amplify the received beat frequency and to select through its tank circuit GL6 the frequency to which tank circuit GL6 is tuned, suppressing other frequencies. The amplified output from tube W6 is impressed through conductor 264 including blocking condenser 265 upon the input impedance 262 of audion tube W7 which further amplifies and through its tank circuits CL", GL7 exercises a further selective action on the impressed beat frequencies. As a result, the reception channel selector selects from the beat frequencies derived from the reception beat detector a beat frequency current having a frequency corresponding to the frequency of the particular subchannels. The selected beat frequency is at the same time amplified so that it is in sufficient strength for utilization in the further apparatus.

The output of the reception channel selector is impressed through an input impedance 271 upon a reception channel amplifier RCA which comprises an audion tube W8 having a cathode 272, an anode 273 and control grid 274, with the associated cathode-heating source 275, plate current source 276, audio frequency choke coil 277 and by-pass condenser 278. The amplified output of the audion tube W8 is then passed through a reception channel rectifier unit RGR comprising a double wave rectifier tube W9 and an amplifier tube W10. The rectifier tube W9 comprises double wave cathodes 281 and two anodes 282 cooperating therewith. An audio frequency transformer 284 has a primary winding 285 connected to the output terminals of the amplifier tube W8, and a mid-tap secondary winding 286 connected to the anodes 282 of the rectifier tube W9. The rectified output is then derived through conductors connected to the cathodes 281 and to the mid-tap of the secondary transformer winding 286, and impressedupon the input impedance 2870f the amplifier tube W10 having a relay of an automatic telegraph such as used for wire telegraphy.

Monitoring apparatus may be connected to the output circuit of the audion tube W8 of the reception channel amplifier, as by means of a jack 297, or by means of a secondary winding of a transformer 298 connected. across the output terminals of audion tube W8.

In operation of the receiving system described above, the modulated impulses reaching the aerial AR of the receiver produce a circulation of current in the receiver antenna. These currents are amplified in the amplifier tube W1, which, as pointed out above, is not critically selective. The amplified oscillations are then impressed on the reception. beat detector RED where a local oscillation is combined with the received signals to produce a beat note which is then amplified in the several amplifying stages of the reception beat amplifier REA. The amplified beat frequency currents are then impressed upon the several stages of the reception channel selector RCS Where the beat frequency currents having the frequency of a particular subchannel are selected and amplified and then impressed upon the reception channel amplifier RCA for further amplification. The output of the latter amplifier is then rectified through the rectifier tube W9 and after further amplification inthe tube W16 the signalling currents so derived are impressed upon the relay RE for actuating the telegraph recording or similar apparatus at the receiving station.

The arrangement described above is particularly useful when employed for the reception of signals of a number of subchannels. As shown in the drawings, the receiving system may be arranged for reception of signals transmitted, for

instance, on five adjacent subchannels corre sponding in this particular example to the five subchannels of the transmitting stations, i. e., for subchannel frequencies of 5,873.50

respectively. For such multiple channel receiving system I do not employ a complete set of re ceiving apparatus as described above for each subchannel, but I employ the reception input amplifier, reception beat detector and reception beat amplifier in common for the several subcha'nnels. With such arrangement, the circuits and the elements of the reception input amplifier RIA, reception beat detector RED and reception beat amplifier REA are so designed and correlated as to be substantially equally sensitive to high frequency signals of all the five subchannels that are to be picked up by the particular receiving apparatus.

Assuming, for instance, that the transmitting apparatus described in application Serial No. 417,684, filed December 31, 1929, radiates a high frequency output which is a combination of sigrial-modulated energy of the five subchannels, C1, C2, C3, or, C5 of the transmitting station, and that such modulated combined five subchannel output is received by the antenna AR of the receiving system, the input into the receiving aerial AR is then amplified in the reception input amplifier RIA and impressed on the radio beat detector RBD. The frequency of the local oscillation of the reception beat detector is-so chosen as to give in combination with any of the five frequencies of the five subchannels of the transmitting station an audio beat frequency in the same way as the monitor beat oscillator. Thus, in the present instance, the local oscillations of the reception beat detector combined with the incoming signals of the five subchannels of the transmitting apparatus will give an output which is the resultant of five modulated beat frequencies of 1125 cycles, i375 cycles, 262.5 cycles, 3375 cycles and 4125 cycles. The resultant currents of these five beat frequencies are then further amplified in the reception beat amplifier and then impressed through the common conductor 242 upon the reception channel selectors RCS of the five subchannels Cl, (32, C3, C4, C5. A separate reception channel selector ROS, reception channel amplifier RCA, reception channel rectifier RCR and reception channel relay RE is provided for each of the five subchannels.

The tanks of the reception channel selectors ROS of the five subchannels are tuned to the five different beat frequencies corresponding to the frequencies assigned to the five subchannels, that is, to the frequencies of 1125 cycles, 1875 cycles, 2625 cycle 3375 cycles and 4125 cycles, so that each reception channel selector picks out from the combined output of the reception beat amplifier REA impressed upon the common conductor 242 only the currents of the beat frequency corresponding to tie particular channel, and these selected beat-frequency currents are then impressed upon the further apparatus of the particular channel for actuating the recording or other telegraph signalling apparatus.

I have found in practical tests that by utilizing radio receiving systems as described above with transmitting systems such as described in application Ser. No. M1684, very good communication without interference may be obtained along closely spaced subchannels and that by the use of this arrangement, it is possible to obtain within the available radio spectrum a much larger number of communication channels than by the other systems proposed heretofore.

A particular advantage of the system described above is the fact that a plurality of subchannels operating on closely adjacent frequency bands are operated in combination as if they were parts of a single channel in such manner that there is excluded the possibility of interference with other communication channels. This is made possible by the combination of the signalling energy of a plurality of subchannels in the transmitting station and the radiation of a combined Wave representing the resultant of the signalling energy of the five subchannels at the transmitting station; and the cooperation therewith of a receiving arrangement in which the received resultant radiations of the transmitting stations are amplified, stepped down by beat frequency oscillator amplifier and then the resultant beat frequency resolved in its component beat frequencies corresponding to the beat frequencies of the several subchannels.

The invention resides not only in the general arrangement of apparatus and systems as described above but also in the specific arrangements of the apparatus of the various elements of the system which are applicable to a variety of other uses than those described herein. Many modifications of the arrangements and details will suggest themselves to those skilled in the art, and it is accordingly desired that the appended claims be given a broad construction commensurate with the scope of the invention within the art.

I claim:

1. In a radio receiving system, means for intercepting high frequency oscillations, a beat detector comprising a ring circuit having a firs audion tube and a second audion tube adapted to oscillate simultaneously, resonant circuits connected to the terminals of the first tube, nonresonant circuits connected to the terminals of the second tube, and connections from the output terminals of the first tube to the input terminals of the second tube and from the output of the second tube to the input terminals of the first tube to cause continuous recirculation of energy between said tubes in the direction from the output electrodes of said second tube to the input electrodes of said first tube, said resonant circuit being tuned to a frequency differing by a beat note from the frequency of the intercepted signals, connections between said intercepting means and the input of said beat detector to cause said beat detector to produce a local oscillatien combining with the intercepted oscillatory currents to produce a beat oscillation of a frequency equal to the difference between the local frequency and the intercepted frequency, and receiving apparatus actuated by said beat frequency currents.

2. In a radio receiving system, aplurality of channel selectors arranged to operate on a plurality of assigned closely adjacent frequencies, each of said channel selectors having means for selectively amplifying currents of the frequency of the assigned channel and discriminatively suppressing oscillations of the other frequencies including the frequencies of the adjacent channels, receiving apparatus individual to each channel connected to each channel selector for actuation by currents of the assigned channel frequency, intercepting means for intercepting signals of frequencies corresponding to all of said channels, a beat detector comprising a ring circuit including two audion tubes adapted to oscillate simultaneously, resonant circuits associated with one of said tubes, non-resonant circuits as sociated with the other of said tubes, connections from the output of one of said tubes to the input of the other of said tubes arranged to form a continuous reentrant circuit to cause continuous recirculation of energy between said tubes, said resonant circuits being tuned to a frequency differing from the intercepted frequencies by an amount equal to the channel selection frequencies, connections between the intercepting means and the input of said beat detector for causing the latter to produce a beat oscillation resultant of beat frequencies of all of said subchannels, and connections between the beat detector and the channel selectors for impressing the combined output of said beat detector upon said channel selectors to cause the latter to individually select the beat frequencies corresponding to the frequency assigned to each channel and to impress said beat frequencies upon the associated receiving apparatus.

3. In a radio communication system, oscillation intercepting means arranged to intercept oscillations of frequencies extending over a predetermined range of the frequency spectrum, means for impressing upon said intercepting means oscillations which are resultant of independently modulated individual oscillations of a plurality of communication channels embracing adjacent sections of said spectrum range, a beat detector comprising two audion tubes connected mutually, with the output of one of the tubes connected to the input of the other to form a reentrant ring circuit, a tuned resonant circuit connected to one of said tubes for controlling the frequency of generated oscillations and arranged to produce local oscillations combining with said impressed oscillations thereby producing a beat frequency current resulting from combination of beat frequency currents corresponding to the oscillations of the individual channels, connections between the intercepting means and the input of the beat detector, a plurality of channel selectors connected to said beat detector for selectively amplifying beat oscillations corresponding to different sections of said spectrum range as assigned to the different channels, and receiving apparatus individually connected to said channel selectors for independent actuation by the beat notes corresponding to the oscillations of the several channels within the given range of the frequency spectrum.

i. In a radio receiving system, means for in tercepting high frequency oscillations, a beat detector containing, a pair of audion tubes arranged in a ring circuit, resonant circuits connected to one of said tubes, non-resonant circuits connected to the terminals of the other of said tubes, connections between said tubes to cause continuous recirculation of energy between said tubes passing from the output electrodes of said second tube to the input electrodes of said first tube, said resonant circuits adapted to be tuned to a frequency differing by a beat note from the intercepted oscillations, said intercepting means and the input of said beat detector being connected together whereby the latter produces a local oscillation which combines with the intercepted oscillatory current thereby producing a beat of a frequency equal to the difference between the frequency of the local oscillation and that of the intercepted 05- 1 cillation, and translating means connected to the output of said beat detector.

EARL L. KOCH. 

